Cannot Create A Multi Node Swarm In Docker For Mac

Getting Started with Swarm Mode. 02/9/2017. 12 minutes to read.In this article What is “swarm mode”?Swarm mode is a Docker feature that provides built in container orchestration capabilities, including native clustering of Docker hosts and scheduling of container workloads.

These are my notes for running Postgres in a Docker container for use with a local Django or Rails development server running on the host machine (not in Docker). Running in Docker allows keeping my database environment isolated from the rest of my system and allows running multiple versions and instances. Docker 17.06.0-ce-RC5 got announced 5 days back and is available for testing. It brings numerous new features & enablements under this new upcoming release. Few of my favourites includes support for Secrets on Windows, allows specifying a secret location within the container, adds -format option to docker system df command, adds support for placement preference to docker stack deploy, adds.

A group of Docker hosts form a “swarm” cluster when their Docker engines are running together in “swarm mode.” For additional context on swarm mode, refer to. Manager nodes and worker nodesA swarm is composed of two types of container hosts: manager nodes, and worker nodes.

Every swarm is initialized via a manager node, and all Docker CLI commands for controlling and monitoring a swarm must be executed from one of its manager nodes. Manager nodes can be thought of as “keepers” of the Swarm state—together, they form a consensus group that maintains awareness of the state of services running on the swarm, and it’s their job to ensure that the swarm’s actual state always matches its intended state, as defined by the developer or admin. NoteAny given swarm can have multiple manager nodes, but it must always have at least one.Worker nodes are orchestrated by Docker swarm via manager nodes. To join a swarm, a worker node must use a “join token” that was generated by the manager node when the swarm was initialized. Worker nodes simply receive and execute tasks from manager nodes, and so they require (and possess) no awareness of the swarm state. Swarm mode system requirementsAt least one physical or virtual computer system (to use the full functionality of swarm at least two nodes is recommended) running either Windows 10 Creators Update or Windows Server 2016 with all of the latest updates., setup as a container host (see the topic, or for more details on how to get started with Docker containers on Windows 10). Note: Docker Swarm on Windows Server 2016 requiresDocker Engine v1.13.0 or laterOpen ports: The following ports must be available on each host.

On some systems, these ports are open by default. TCP port 2377 for cluster management communications. TCP and UDP port 7946 for communication among nodes. UDP port 4789 for overlay network trafficInitializing a Swarm clusterTo initialize a swarm, simply run the following command from one of your container hosts (replacing with the local IPv4 address of your host machine): # Initialize a swarmC: docker swarm init -advertise-addr= -listen-addr:2377When this command is run from a given container host, the Docker engine on that host begins running in swarm mode as a manager node.

Adding nodes to a swarmMultiple nodes are not required to leverage swarm mode and overlay networking mode features. All swarm/overlay features can be used with a single host running in swarm mode (i.e.

A manager node, put into swarm mode with the docker swarm init command). Adding workers to a swarmOnce a swarm has been initialized from a manager node, other hosts can be added to the swarm as workers with another simple command: C: docker swarm join -token Here, is the local IP address of a swarm manager node, and is the worker join-token provided as output by the docker swarm init command that was run from the manager node. The join-token can also be obtained by running one of the following commands from the manager node after the swarm has been initialized: # Get the full command required to join a worker node to the swarmC: docker swarm join-token worker# Get only the join-token needed to join a worker node to the swarmC: docker swarm join-token worker -qAdding managers to a swarmAdditional manager nodes can be added to a swarm cluster with the following command: C: docker swarm join -token Again, is the local IP address of a swarm manager node.

The join token, is a manager join-token for the swarm, which can be obtained by running one of the following commands from an existing manager node: # Get the full command required to join a.manager. node to the swarmC: docker swarm join-token manager# Get only the join-token needed to join a.manager. node to the swarmC: docker swarm join-token manager -qCreating an overlay networkOnce a swarm cluster has been configured, overlay networks can be created on the swarm. An overlay network can be created by running the following command from a swarm manager node: # Create an overlay networkC: docker network create -driver=overlay Here, is the name you'd like to give to your network.

Deploying services to a swarmOnce an overlay network has been created, services can be created and attached to the network. A service is created with the following syntax: # Deploy a service to the swarmC: docker service create -name= -endpoint-mode dnsrr -network= COMMAND ARGSHere, is the name you'd like to give to the service-this is the name you will use to reference the service via service discovery (which uses Docker's native DNS server). Is the name of the network that you would like to connect this service to (for example, 'myOverlayNet'). Is the name of the container image that will defined the service. NoteThe second argument to this command, -endpoint-mode dnsrr, is required to specify to the Docker engine that the DNS Round Robin policy will be used to balance network traffic across service container endpoints. Currently, DNS Round-Robin is the only load balancing strategy supported on Windows Server 2016.

For Windows docker hosts is supported on Windows Server 2019 (and above), but not on Windows Server 2016. Users seeking an alternative load balancing strategy on Windows Server 2016 today can setup an external load balancer (e.g. NGINX) and use Swarm’s to expose container host ports over which to balance traffic. Scaling a serviceOnce a service is deployed to a swarm cluster, the container instances composing that service are deployed across the cluster. By default, the number of container instances backing a service—the number of “replicas,” or “tasks” for a service—is one. However, a service can be created with multiple tasks using the -replicas option to the docker service create command, or by scaling the service after it has been created.Service scalability is a key benefit offered by Docker Swarm, and it, too, can be leveraged with a single Docker command: C: docker service scale =Here, is the name of the service being scaled, and is the number of tasks, or container instances, to which the service is being scaled.

Viewing the swarm stateThere are several useful commands for viewing the state of a swarm and the services running on the swarm. List swarm nodesUse the following command to see a list of the nodes currently joined to a swarm, including informaiton on the state of each node. This command must be run from a manager node.

C: docker node lsIn the output of this command, you will notice one of the nodes marked with an asterisk (.); the asterisk simply indicates the current node-the node from which the docker node ls command was run. List networksUse the following command to see a list of the networks that exist on a given node.

To see overlay networks, this command must be run from a manager node running in swarm mode. C: docker network lsList servicesUse the following command to see a list of the services currently running on a swarm, including information on their state.

C: docker service lsList the container instances that define a serviceUse the following command to see details on the container instances running for a given service. The output for this command includes the IDs and nodes upon which each container is running, as well as infromation on the state of the containers. C: docker service ps Linux+Windows mixed-OS clustersRecently, a member of our team posted a short, three-part demo on how to set up a Windows+Linux mixed-OS application using Docker Swarm. It's a great place to get started if you're new to Docker Swarm, or to using it to run mixed-OS applications.

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The goal of this example is to show you how to get a Node.js application into aDocker container. The guide is intended for development, and not for aproduction deployment. The guide also assumes you have a working Dockerinstallation and a basicunderstanding of how a Node.js application is structured.

In the first part of this guide we will create a simple web application inNode.js, then we will build a Docker image for that application, and lastly wewill instantiate a container from that image.

Docker allows you to package an application with its environment and all of its dependencies into a'box', called a container. Usually, a container consists of an application running in a stripped-to-basics version of a Linux operating system. An image is the blueprint for a container, a container is a running instance of an image.

Create the Node.js app

First, create a new directory where all the files would live. In this directorycreate a package.json file that describes your app and its dependencies:

With your new package.json file, run npm install. If you are using npmversion 5 or later, this will generate a package-lock.json file which will be copiedto your Docker image.

Then, create a server.js file that defines a web app using theExpress.js framework:

In the next steps, we'll look at how you can run this app inside a Dockercontainer using the official Docker image. First, you'll need to build a Dockerimage of your app.

Creating a Dockerfile

Create an empty file called Dockerfile:

Open the Dockerfile in your favorite text editor

The first thing we need to do is define from what image we want to build from.Here we will use the latest LTS (long term support) version 12 of nodeavailable from the Docker Hub:

Next we create a directory to hold the application code inside the image, thiswill be the working directory for your application:

This image comes with Node.js and NPM already installed so the next thing weneed to do is to install your app dependencies using the npm binary. Pleasenote that if you are using npm version 4 or earlier a package-lock.jsonfile will not be generated.

Note that, rather than copying the entire working directory, we are only copyingthe package.json file. This allows us to take advantage of cached Dockerlayers. bitJudo has a good explanation of thishere.Furthermore, the npm ci command, specified in the comments, helps provide faster, reliable, reproducible builds for production environments.You can read more about this here.

To bundle your app's source code inside the Docker image, use the COPYinstruction:

Your app binds to port 8080 so you'll use the EXPOSE instruction to have itmapped by the docker daemon:

Last but not least, define the command to run your app using CMD which definesyour runtime. Here we will use node server.js to start your server:

Your Dockerfile should now look like this:

.dockerignore file

Create a .dockerignore file in the same directory as your Dockerfilewith following content:

This will prevent your local modules and debug logs from being copied onto yourDocker image and possibly overwriting modules installed within your image.

Building your image

Go to the directory that has your Dockerfile and run the following command tobuild the Docker image. The -t flag lets you tag your image so it's easier tofind later using the docker images command:

Your image will now be listed by Docker:

Run the image

Running your image with -d runs the container in detached mode, leaving thecontainer running in the background. The -p flag redirects a public port to aprivate port inside the container. Run the image you previously built:

Print the output of your app:

If you need to go inside the container you can use the exec command:

Test

To test your app, get the port of your app that Docker mapped:

In the example above, Docker mapped the 8080 port inside of the container tothe port 49160 on your machine.

Now you can call your app using curl (install if needed via: sudo apt-getinstall curl):

We hope this tutorial helped you get up and running a simple Node.js applicationon Docker.

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You can find more information about Docker and Node.js on Docker in thefollowing places: